feat: add a guide on materialized ctes to query-data

use-timescale/query-data/cte.md

@@ -0,0 +1,38 @@
+---
+title: Get faster JOIN queries with Common Table Expressions (CTEs)
+excerpt: Speed up JOIN queries by materializing hypertable queries before joining to other tables
+products: [cloud, mst, self_hosted]
+keywords: [queries, JOIN, CTE]
+---
+
+# Get faster JOIN queries with Common Table Expressions (CTEs)
+
+Imagine I have a query that joins a hypertable to some other table on a shared key.
+
+```sql
+    SELECT timestamp, 
+      FROM hypertable as h
+      JOIN related_table as rt
+        ON rt.id = h.related_table_id
+     WHERE h.timestamp BETWEEN '2024-10-10 00:00:00' AND '2024-10-17 00:00:00'
+```
+
+If I `EXPLAIN` this query, I might see that the `Postgres` query planner decides that it should perform a `NestedJoin` between these two tables and thus query the hypertable multiple times.  Even if the hypertable is well indexed, if the hypertable is large this query will be slower than if `Postgres` had looked up the hypertable once.  How do we force a once-only lookup?
+
+We can use materialized Common Table Expressions (CTEs)!
+
+If I split my query into two parts using CTEs, I can `materialize` the hypertable lookup and thus force `Postgres` to perform only one hypertable lookup.
+
+```sql
+WITH cached_query AS materialized (
+  SELECT *
+    FROM hypertable
+   WHERE BETWEEN '2024-10-10 00:00:00' AND '2024-10-17 00:00:00'
+)
+  SELECT *
+    FROM cached_query as c
+    JOIN related_table as rt
+      ON rt.id = h.related_table_id
+```
+
+Now if I run `EXPLAIN` once again I can prove that this query performs only one lookup.  Depending on the size of your hypertable, this could result in a multi-hour query taking mere seconds.

use-timescale/query-data/index.md

@@ -14,10 +14,12 @@ use [PopSQL][popsql] to work on data with centralized SQL queries, interactive v
 *   [About querying data][about-querying-data]
 *   [Select data with `SELECT`][selecting-data]
 *   [Get faster `DISTINCT` queries with SkipScan][skipscan]
+*   [Get faster `JOIN` queries with `Materialized Common Table Expressions (CTEs)][cte]
 *   [Perform advanced analytic queries][advanced-analytics]
 
 [about-querying-data]: /use-timescale/:currentVersion:/query-data/about-query-data/
 [advanced-analytics]: /use-timescale/:currentVersion:/query-data/advanced-analytic-queries/
 [selecting-data]: /use-timescale/:currentVersion:/query-data/select/
 [skipscan]: /use-timescale/:currentVersion:/query-data/skipscan/
+[cte]: /use-timescale/:currentVersion:/query-data/cte/
 [popsql]: /getting-started/:currentVersion:/run-queries-from-console/